Tau-square



T sQUARE.

APPLICATION FILED DEC- 4, 1920.

Patented June 14, 1921.

UNITED STATES MARTIN D. DAVIS, 0F DALEVILLE, INDIANA.

'r-sQUARE.

Specification of Letters Patent.

Application filed December 4, 1920. Serial No. 428,273.

To all e0 hom it may concern.'

Be it known that I, IVIARTIN D. DAVIS, a citizen of the United States, residingv at Daleville, in the county of Delaware and State of Indiana, have invented certain new and useful Improvements in TSquares, of which the following is a specification.

This invention relates to Tsquares of that type in which the blade is pivotally mounted upon the head so that it may be set at any desired angle thereto and the object of the present invention is to provide an improved mounting for the blade whereby it may be firmly secured in a set position without unduly adding to the weight of the instrument 0r to the cost of manufacturing the same. The invention is illustrated in the accompanying drawings and will be hereinafter fully described, the novel features being particularly pointed out ,in the appended claims.

Figure 1 is a plan view of'a T-square embodying my present invention;

Fig. 2 is a section on the line 2-2 of F ig. l; Y

, Fig. 3 is a section on the line 3 3 of Fig. l l

Fig. il is a detail plan View of the locking washer.

The head 1 and blade 2 may be of any preferred material or dimensions, the head being preferably provided with an arcuate portion 3 intermediate its ends on its rear edge and having a graduated scale 4 displayed upon its upper surface immediately adjacent the said arcute portion. This scale may be marked directly upon the head, but

n*I prefer to form it upon an arcuate strip of Celluloid or other material which strip may be secured to the head by screws 5 inserted through its ends, as will be readily understood. The blade has its pivotal end also formed on an arc concentric with its pivot and adapted to rest closely against the scale 41.-, as shown at 6 in Fig. 1. This arcuate end of the blade will preferably have a scale 7 marked thereon and the scale 7 will be so calibrated that six of its divisions will be equal to five divisions of the scale 4t and will constitute a Vernier.

llithin the head 1, I form a circular recess 8 and in the base of the said recess I secure a disk 9 which will preferably be of fiber, although it may be of rubber or any other friction-creating material. This disk will be secured firmly in the base of the recess 8, preferably by applying glue thereto and a shallow smaller cavity 10 will be formed concentric in the base of the recess 8 to receive the head 11 of a stud bolt 12. This bolt 12 extends through arcentral opening in the disk 9 and is secured thereto by one or more pins 13 inserted through the base of the bolt and the disk, as clearly shown in Fig. 2. The blade is provided with an opening, indicated at 14, which receives a locking washer 15 and to the under side of the blade, bridging the opening 14 and the said washer 15, I secure a disk 1G corresponding in all respects to the disk 9. This disk 16 may be secured to the blade in any desired manner but I prefer to employ glue or some other adhesive having nonwarping qualities and, as clearly shown in Figs. 2 and 3, the disks 9 and 16 are in intimate contact and together fill the recess 8 in the head. The locking washer 15 is provided with a lug or tooth 17 on its inner periphery which engages a longitudinal groove 18 in the side of the stud bolt 12 so that relative turning movement of the said washer and the bolt will be prevented. The bolt is constructed with a reduced threaded extremity 19 so that an annular' shoulder 20 is provided flush with the upper surface of the locking washer and a nut 21 is fitted upon the threaded extremity of the bolt and bears upon the locking washer, as clearly shown in Figs. 2 and 3.

The friction disks 9 and 1b are provided with openings therethrough and the blade is provided with an opening 22 adapted to register with the said openings in the friction disk when the blade is at a right angle to the head which is the position in which the instrument is most frequently set. To hold the blade at a right angle to the head, I provide a plug 23 of metal which is tapered, as shown clearly in Fig. 3, and may be readily engaged in the openings mentioned when the blade is in its usual position at a right angle to the head. The provision of this plug and the openings in which it engages facilitates the setting of the blade at a right angle to the head inasmuch as it is not necessary to closely watch the finely marked graduations of the scales upon the blade and the head, but it is suiicient to bring the openings in the blade and its friction disk into axial alinernent with the opening in the friction disk in the head whereupon the plug Patented June 14, 1921.

may be inserted and the parts will be in the desired position. rlhis arrangement will also be found advantageous in the event that either of the arcuate scales should be broke or become effaced for any reason. l

When it is desired to set the blade at an oblique angle to the head, the plug 23 is withdrawn and the nut 2l is loosened,after which the blade may be easily swung about the pivot bolt and when it has been brought into the desired position 'the nut is turned home so that the pressure exerted by it upon the locking` washer and through the same upon the friction disk 16 will firmly bind said disk upon the friction disk 9 and thereby hold the blade in its set position.

lt will be readily noted that myu improved mechanism is exceedingly simple and is light soV that it does not add any appreciable weight to the instrument and it will also be noted that the holding parts VareA housed within the head and covered by the blade so that they are not apt to get out of order and do not detract from theappearance of the instrument. Villien the nut 2l has been turned home,the blade will be firmly held in its set position and the pitch of the threaded extremity of the bolt and of the nut should be such that a slight turn of the nut will be suii'icient to drive it home or to release the blade to permit a readjustment thereof. es the locking washer cannot turn about the pivot stud bolt the rotation of the nut will quickly establish the required binding 'engagement between the friction disks to hold the head and the blade in the desired relation.

Having thus described the invention, what is claimed as 4new is:

l. In a T-square, the combinationl of a head having a recess therein, a blade pivotally mounted upon the head concentric with said recess, and opposed friction disks housed within the recess of the head and secured respectively to the head and the blade.

2. ln a T-square, the combination with ai blade, and a head having a recess therein,

of a stud bolt fixed within the recess and passingthrough the blade whereby the blade .will be pivotally mounted upon said bolt,

opposed friction disks fitted within the re- Vcess'in the head and carried respectively by the head and the blade, and a lockingvnut mounted upon the bolt at the outer side of the blade and adapted to establish binding frictional engagement between the said friction disks.

3. In a T-square, the combination of a head having a recess therein, a blade disposed upon the head andV having an opening therethrough, a stud bolt secured concentrically in the recess in the head and extending through the opening in the blade, saidy bolt being provided witha longitudinal groove, a friction disk secured to and encircling said bolt and fixed in the recess in the head, a second friction disk disposed concentrically about the bolt and secured to the under side of the blade and housed within the recess in the head whereby it may lie upon the firstmentioned friction disk, a locking washer fitted in the opening in the blade and having an internal lug engaging the longitudinal groove in the bolt, and a locking nut fitted over the extremity of the boltV and bearing upon said locking washer.

d. ln a T-square, the combination of a head having a recess therein, a friction disk seated in said recess, a blade pivotally mounted on the head concentric to said recess, a friction diskA on the blade fitting within the recess in the head and bearing upon the friction disk therein, the blade and the friction disk therein having each an ings to hold the blade at a right angle to the head.

ln testimony whereof I affix my signature.

MARTIN D. Davis. VL. SQ] 

